In the past, computers generally operated on files of relatively simple data, such as a program object file or a data file containing ASCII text. Now computers operate on complex systems of interrelated components. For example, a program may comprise dozens of modules that are dynamically loaded and released as needed. Whereas a document, such as a web page, may be composed of multiple interrelated files, including text, images, audio, video, links to other documents, and executable routines.
To better cope with the explosion in complexity, many developers employ component-based development techniques. Using these techniques, complex systems can be constructed by combining simpler, robust components. For example, a web page may be composed of a template component that defines the basic look and feel of the web site as a whole, combined with a text component that specifies the textual content to be laid out according to the template.
Generally, components are units of code or content that are independently deployable, and that may be used with other components to build systems, such as software applications and digital content. Components may also be used to build other components. A component should be well-separated from its environment and from other components, should be self-contained, and should have a well-defined interface. The interface of a software component typically includes definitions of the publically accessible features of the component, such as functions, classes, or global variables. These portions of the external interface are referred to as the functional or programmatic interface of the software component because they define how the software component functions. Because the interface determines how a component may be invoked, a component based system may allow multiple component implementations to express the same interface.
In addition to the functional aspects of a component specified in the component interface, components often have nonfunctional attributes as well. For example, the name of the programmer that created a software component, it's revision history, known bugs, a copyright notice, and a vendor identifier, are nonfunctional attributes of a component. As used herein, such nonfunctional or informational component attributes are referred to as meta-data.
Although some component systems, such as those provided by the Java™ programming language, permit meta-data such as a vendor name or a version number to be associated with a component, the meta-data is often limited to a fixed set and typically cannot be extended. Other systems, such as the Component Object Model (COM) architecture, by Microsoft Corporation of Richmond, Washington do not provide a mechanism for associating arbitrary meta-data with a component. It would therefore be desirable to provide a mechanism for associating arbitrary meta-data with digital components.
However, statically associating arbitrary meta-data with a digital component may not be sufficient in a complex system incorporating many components. In some instances, it may be important to be able to add, delete, or update meta-data associated with a component. Meta-data associated with a component may include information that is apt to change over time, such as information identifying a web site or telephone number that may be used to obtain technical support about proper use of the component. Or, interface specifications may become deprecated or altered. It would therefore be desirable to provide a mechanism for modifying component meta-data.
In addition to information such as providing vendor identification, references to technical support, and the like, meta-data may also be used to indicate that a component complies with a relevant standard or meets certain safety requirements. For example, a third party certification organization may add a meta-data element to a component indicating that the component complies with the POSIX specification or that the manufacturer is ISO 9000 certified. Such meta-data may only be relied upon if it is secure from tampering and alteration. However, such meta-data may need to be changed or revoked, if, for example, an area of non-compliance were found after the original certification was given. It would therefore be desirable to provide methods for securing meta-data against tampering while providing for authorized changes to the meta-data.